/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 */

package java.io;

import java.io.ObjectStreamClass.WeakClassKey;
import java.lang.ref.ReferenceQueue;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import static java.io.ObjectStreamClass.processQueue;

import java.io.SerialCallbackContext;
import sun.reflect.misc.ReflectUtil;

/**
 * An ObjectOutputStream writes primitive data types and graphs of Java objects
 * to an OutputStream.  The objects can be read (reconstituted) using an
 * ObjectInputStream.  Persistent storage of objects can be accomplished by
 * using a file for the stream.  If the stream is a network socket stream, the
 * objects can be reconstituted on another host or in another process.
 *
 * <p>Only objects that support the java.io.Serializable interface can be
 * written to streams.  The class of each serializable object is encoded
 * including the class name and signature of the class, the values of the
 * object's fields and arrays, and the closure of any other objects referenced
 * from the initial objects.
 *
 * <p>The method writeObject is used to write an object to the stream.  Any
 * object, including Strings and arrays, is written with writeObject. Multiple
 * objects or primitives can be written to the stream.  The objects must be
 * read back from the corresponding ObjectInputstream with the same types and
 * in the same order as they were written.
 *
 * <p>Primitive data types can also be written to the stream using the
 * appropriate methods from DataOutput. Strings can also be written using the
 * writeUTF method.
 *
 * <p>The default serialization mechanism for an object writes the class of the
 * object, the class signature, and the values of all non-transient and
 * non-static fields.  References to other objects (except in transient or
 * static fields) cause those objects to be written also. Multiple references
 * to a single object are encoded using a reference sharing mechanism so that
 * graphs of objects can be restored to the same shape as when the original was
 * written.
 *
 * <p>For example to write an object that can be read by the example in
 * ObjectInputStream:
 * <br>
 * <pre>
 *      FileOutputStream fos = new FileOutputStream("t.tmp");
 *      ObjectOutputStream oos = new ObjectOutputStream(fos);
 *
 *      oos.writeInt(12345);
 *      oos.writeObject("Today");
 *      oos.writeObject(new Date());
 *
 *      oos.close();
 * </pre>
 *
 * <p>Classes that require special handling during the serialization and
 * deserialization process must implement special methods with these exact
 * signatures:
 * <br>
 * <pre>
 * private void readObject(java.io.ObjectInputStream stream)
 *     throws IOException, ClassNotFoundException;
 * private void writeObject(java.io.ObjectOutputStream stream)
 *     throws IOException
 * private void readObjectNoData()
 *     throws ObjectStreamException;
 * </pre>
 *
 * <p>The writeObject method is responsible for writing the state of the object
 * for its particular class so that the corresponding readObject method can
 * restore it.  The method does not need to concern itself with the state
 * belonging to the object's superclasses or subclasses.  State is saved by
 * writing the individual fields to the ObjectOutputStream using the
 * writeObject method or by using the methods for primitive data types
 * supported by DataOutput.
 *
 * <p>Serialization does not write out the fields of any object that does not
 * implement the java.io.Serializable interface.  Subclasses of Objects that
 * are not serializable can be serializable. In this case the non-serializable
 * class must have a no-arg constructor to allow its fields to be initialized.
 * In this case it is the responsibility of the subclass to save and restore
 * the state of the non-serializable class. It is frequently the case that the
 * fields of that class are accessible (public, package, or protected) or that
 * there are get and set methods that can be used to restore the state.
 *
 * <p>Serialization of an object can be prevented by implementing writeObject
 * and readObject methods that throw the NotSerializableException.  The
 * exception will be caught by the ObjectOutputStream and abort the
 * serialization process.
 *
 * <p>Implementing the Externalizable interface allows the object to assume
 * complete control over the contents and format of the object's serialized
 * form.  The methods of the Externalizable interface, writeExternal and
 * readExternal, are called to save and restore the objects state.  When
 * implemented by a class they can write and read their own state using all of
 * the methods of ObjectOutput and ObjectInput.  It is the responsibility of
 * the objects to handle any versioning that occurs.
 *
 * <p>Enum constants are serialized differently than ordinary serializable or
 * externalizable objects.  The serialized form of an enum constant consists
 * solely of its name; field values of the constant are not transmitted.  To
 * serialize an enum constant, ObjectOutputStream writes the string returned by
 * the constant's name method.  Like other serializable or externalizable
 * objects, enum constants can function as the targets of back references
 * appearing subsequently in the serialization stream.  The process by which
 * enum constants are serialized cannot be customized; any class-specific
 * writeObject and writeReplace methods defined by enum types are ignored
 * during serialization.  Similarly, any serialPersistentFields or
 * serialVersionUID field declarations are also ignored--all enum types have a
 * fixed serialVersionUID of 0L.
 *
 * <p>Primitive data, excluding serializable fields and externalizable data, is
 * written to the ObjectOutputStream in block-data records. A block data record
 * is composed of a header and data. The block data header consists of a marker
 * and the number of bytes to follow the header.  Consecutive primitive data
 * writes are merged into one block-data record.  The blocking factor used for
 * a block-data record will be 1024 bytes.  Each block-data record will be
 * filled up to 1024 bytes, or be written whenever there is a termination of
 * block-data mode.  Calls to the ObjectOutputStream methods writeObject,
 * defaultWriteObject and writeFields initially terminate any existing
 * block-data record.
 *
 * @author Mike Warres
 * @author Roger Riggs
 * @see java.io.DataOutput
 * @see java.io.ObjectInputStream
 * @see java.io.Serializable
 * @see java.io.Externalizable
 * @see <a href="../../../platform/serialization/spec/output.html">Object Serialization
 * Specification, Section 2, Object Output Classes</a>
 * @since JDK1.1
 */
public class ObjectOutputStream
    extends OutputStream implements ObjectOutput, ObjectStreamConstants {

  private static class Caches {

    /**
     * cache of subclass security audit results
     */
    static final ConcurrentMap<WeakClassKey, Boolean> subclassAudits =
        new ConcurrentHashMap<>();

    /**
     * queue for WeakReferences to audited subclasses
     */
    static final ReferenceQueue<Class<?>> subclassAuditsQueue =
        new ReferenceQueue<>();
  }

  /**
   * filter stream for handling block data conversion
   */
  private final BlockDataOutputStream bout;
  /**
   * obj -> wire handle map
   */
  private final HandleTable handles;
  /**
   * obj -> replacement obj map
   */
  private final ReplaceTable subs;
  /**
   * stream protocol version
   */
  private int protocol = PROTOCOL_VERSION_2;
  /**
   * recursion depth
   */
  private int depth;

  /**
   * buffer for writing primitive field values
   */
  private byte[] primVals;

  /**
   * if true, invoke writeObjectOverride() instead of writeObject()
   */
  private final boolean enableOverride;
  /**
   * if true, invoke replaceObject()
   */
  private boolean enableReplace;

  // values below valid only during upcalls to writeObject()/writeExternal()
  /**
   * Context during upcalls to class-defined writeObject methods; holds
   * object currently being serialized and descriptor for current class.
   * Null when not during writeObject upcall.
   */
  private SerialCallbackContext curContext;
  /**
   * current PutField object
   */
  private PutFieldImpl curPut;

  /**
   * custom storage for debug trace info
   */
  private final DebugTraceInfoStack debugInfoStack;

  /**
   * value of "sun.io.serialization.extendedDebugInfo" property,
   * as true or false for extended information about exception's place
   */
  private static final boolean extendedDebugInfo =
      java.security.AccessController.doPrivileged(
          new sun.security.action.GetBooleanAction(
              "sun.io.serialization.extendedDebugInfo")).booleanValue();

  /**
   * Creates an ObjectOutputStream that writes to the specified OutputStream.
   * This constructor writes the serialization stream header to the
   * underlying stream; callers may wish to flush the stream immediately to
   * ensure that constructors for receiving ObjectInputStreams will not block
   * when reading the header.
   *
   * <p>If a security manager is installed, this constructor will check for
   * the "enableSubclassImplementation" SerializablePermission when invoked
   * directly or indirectly by the constructor of a subclass which overrides
   * the ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared
   * methods.
   *
   * @param out output stream to write to
   * @throws IOException if an I/O error occurs while writing stream header
   * @throws SecurityException if untrusted subclass illegally overrides security-sensitive methods
   * @throws NullPointerException if <code>out</code> is <code>null</code>
   * @see ObjectOutputStream#ObjectOutputStream()
   * @see ObjectOutputStream#putFields()
   * @see ObjectInputStream#ObjectInputStream(InputStream)
   * @since 1.4
   */
  public ObjectOutputStream(OutputStream out) throws IOException {
    verifySubclass();
    bout = new BlockDataOutputStream(out);
    handles = new HandleTable(10, (float) 3.00);
    subs = new ReplaceTable(10, (float) 3.00);
    enableOverride = false;
    writeStreamHeader();
    bout.setBlockDataMode(true);
    if (extendedDebugInfo) {
      debugInfoStack = new DebugTraceInfoStack();
    } else {
      debugInfoStack = null;
    }
  }

  /**
   * Provide a way for subclasses that are completely reimplementing
   * ObjectOutputStream to not have to allocate private data just used by
   * this implementation of ObjectOutputStream.
   *
   * <p>If there is a security manager installed, this method first calls the
   * security manager's <code>checkPermission</code> method with a
   * <code>SerializablePermission("enableSubclassImplementation")</code>
   * permission to ensure it's ok to enable subclassing.
   *
   * @throws SecurityException if a security manager exists and its <code>checkPermission</code>
   * method denies enabling subclassing.
   * @throws IOException if an I/O error occurs while creating this stream
   * @see SecurityManager#checkPermission
   * @see java.io.SerializablePermission
   */
  protected ObjectOutputStream() throws IOException, SecurityException {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
    }
    bout = null;
    handles = null;
    subs = null;
    enableOverride = true;
    debugInfoStack = null;
  }

  /**
   * Specify stream protocol version to use when writing the stream.
   *
   * <p>This routine provides a hook to enable the current version of
   * Serialization to write in a format that is backwards compatible to a
   * previous version of the stream format.
   *
   * <p>Every effort will be made to avoid introducing additional
   * backwards incompatibilities; however, sometimes there is no
   * other alternative.
   *
   * @param version use ProtocolVersion from java.io.ObjectStreamConstants.
   * @throws IllegalStateException if called after any objects have been serialized.
   * @throws IllegalArgumentException if invalid version is passed in.
   * @throws IOException if I/O errors occur
   * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
   * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_2
   * @since 1.2
   */
  public void useProtocolVersion(int version) throws IOException {
    if (handles.size() != 0) {
      // REMIND: implement better check for pristine stream?
      throw new IllegalStateException("stream non-empty");
    }
    switch (version) {
      case PROTOCOL_VERSION_1:
      case PROTOCOL_VERSION_2:
        protocol = version;
        break;

      default:
        throw new IllegalArgumentException(
            "unknown version: " + version);
    }
  }

  /**
   * Write the specified object to the ObjectOutputStream.  The class of the
   * object, the signature of the class, and the values of the non-transient
   * and non-static fields of the class and all of its supertypes are
   * written.  Default serialization for a class can be overridden using the
   * writeObject and the readObject methods.  Objects referenced by this
   * object are written transitively so that a complete equivalent graph of
   * objects can be reconstructed by an ObjectInputStream.
   *
   * <p>Exceptions are thrown for problems with the OutputStream and for
   * classes that should not be serialized.  All exceptions are fatal to the
   * OutputStream, which is left in an indeterminate state, and it is up to
   * the caller to ignore or recover the stream state.
   *
   * @throws InvalidClassException Something is wrong with a class used by serialization.
   * @throws NotSerializableException Some object to be serialized does not implement the
   * java.io.Serializable interface.
   * @throws IOException Any exception thrown by the underlying OutputStream.
   */
  public final void writeObject(Object obj) throws IOException {
    if (enableOverride) {
      writeObjectOverride(obj);
      return;
    }
    try {
      writeObject0(obj, false);
    } catch (IOException ex) {
      if (depth == 0) {
        writeFatalException(ex);
      }
      throw ex;
    }
  }

  /**
   * Method used by subclasses to override the default writeObject method.
   * This method is called by trusted subclasses of ObjectInputStream that
   * constructed ObjectInputStream using the protected no-arg constructor.
   * The subclass is expected to provide an override method with the modifier
   * "final".
   *
   * @param obj object to be written to the underlying stream
   * @throws IOException if there are I/O errors while writing to the underlying stream
   * @see #ObjectOutputStream()
   * @see #writeObject(Object)
   * @since 1.2
   */
  protected void writeObjectOverride(Object obj) throws IOException {
  }

  /**
   * Writes an "unshared" object to the ObjectOutputStream.  This method is
   * identical to writeObject, except that it always writes the given object
   * as a new, unique object in the stream (as opposed to a back-reference
   * pointing to a previously serialized instance).  Specifically:
   * <ul>
   * <li>An object written via writeUnshared is always serialized in the
   * same manner as a newly appearing object (an object that has not
   * been written to the stream yet), regardless of whether or not the
   * object has been written previously.
   *
   * <li>If writeObject is used to write an object that has been previously
   * written with writeUnshared, the previous writeUnshared operation
   * is treated as if it were a write of a separate object.  In other
   * words, ObjectOutputStream will never generate back-references to
   * object data written by calls to writeUnshared.
   * </ul>
   * While writing an object via writeUnshared does not in itself guarantee a
   * unique reference to the object when it is deserialized, it allows a
   * single object to be defined multiple times in a stream, so that multiple
   * calls to readUnshared by the receiver will not conflict.  Note that the
   * rules described above only apply to the base-level object written with
   * writeUnshared, and not to any transitively referenced sub-objects in the
   * object graph to be serialized.
   *
   * <p>ObjectOutputStream subclasses which override this method can only be
   * constructed in security contexts possessing the
   * "enableSubclassImplementation" SerializablePermission; any attempt to
   * instantiate such a subclass without this permission will cause a
   * SecurityException to be thrown.
   *
   * @param obj object to write to stream
   * @throws NotSerializableException if an object in the graph to be serialized does not implement
   * the Serializable interface
   * @throws InvalidClassException if a problem exists with the class of an object to be serialized
   * @throws IOException if an I/O error occurs during serialization
   * @since 1.4
   */
  public void writeUnshared(Object obj) throws IOException {
    try {
      writeObject0(obj, true);
    } catch (IOException ex) {
      if (depth == 0) {
        writeFatalException(ex);
      }
      throw ex;
    }
  }

  /**
   * Write the non-static and non-transient fields of the current class to
   * this stream.  This may only be called from the writeObject method of the
   * class being serialized. It will throw the NotActiveException if it is
   * called otherwise.
   *
   * @throws IOException if I/O errors occur while writing to the underlying
   * <code>OutputStream</code>
   */
  public void defaultWriteObject() throws IOException {
    SerialCallbackContext ctx = curContext;
    if (ctx == null) {
      throw new NotActiveException("not in call to writeObject");
    }
    Object curObj = ctx.getObj();
    ObjectStreamClass curDesc = ctx.getDesc();
    bout.setBlockDataMode(false);
    defaultWriteFields(curObj, curDesc);
    bout.setBlockDataMode(true);
  }

  /**
   * Retrieve the object used to buffer persistent fields to be written to
   * the stream.  The fields will be written to the stream when writeFields
   * method is called.
   *
   * @return an instance of the class Putfield that holds the serializable fields
   * @throws IOException if I/O errors occur
   * @since 1.2
   */
  public ObjectOutputStream.PutField putFields() throws IOException {
    if (curPut == null) {
      SerialCallbackContext ctx = curContext;
      if (ctx == null) {
        throw new NotActiveException("not in call to writeObject");
      }
      Object curObj = ctx.getObj();
      ObjectStreamClass curDesc = ctx.getDesc();
      curPut = new PutFieldImpl(curDesc);
    }
    return curPut;
  }

  /**
   * Write the buffered fields to the stream.
   *
   * @throws IOException if I/O errors occur while writing to the underlying stream
   * @throws NotActiveException Called when a classes writeObject method was not called to write the
   * state of the object.
   * @since 1.2
   */
  public void writeFields() throws IOException {
    if (curPut == null) {
      throw new NotActiveException("no current PutField object");
    }
    bout.setBlockDataMode(false);
    curPut.writeFields();
    bout.setBlockDataMode(true);
  }

  /**
   * Reset will disregard the state of any objects already written to the
   * stream.  The state is reset to be the same as a new ObjectOutputStream.
   * The current point in the stream is marked as reset so the corresponding
   * ObjectInputStream will be reset at the same point.  Objects previously
   * written to the stream will not be referred to as already being in the
   * stream.  They will be written to the stream again.
   *
   * @throws IOException if reset() is invoked while serializing an object.
   */
  public void reset() throws IOException {
    if (depth != 0) {
      throw new IOException("stream active");
    }
    bout.setBlockDataMode(false);
    bout.writeByte(TC_RESET);
    clear();
    bout.setBlockDataMode(true);
  }

  /**
   * Subclasses may implement this method to allow class data to be stored in
   * the stream. By default this method does nothing.  The corresponding
   * method in ObjectInputStream is resolveClass.  This method is called
   * exactly once for each unique class in the stream.  The class name and
   * signature will have already been written to the stream.  This method may
   * make free use of the ObjectOutputStream to save any representation of
   * the class it deems suitable (for example, the bytes of the class file).
   * The resolveClass method in the corresponding subclass of
   * ObjectInputStream must read and use any data or objects written by
   * annotateClass.
   *
   * @param cl the class to annotate custom data for
   * @throws IOException Any exception thrown by the underlying OutputStream.
   */
  protected void annotateClass(Class<?> cl) throws IOException {
  }

  /**
   * Subclasses may implement this method to store custom data in the stream
   * along with descriptors for dynamic proxy classes.
   *
   * <p>This method is called exactly once for each unique proxy class
   * descriptor in the stream.  The default implementation of this method in
   * <code>ObjectOutputStream</code> does nothing.
   *
   * <p>The corresponding method in <code>ObjectInputStream</code> is
   * <code>resolveProxyClass</code>.  For a given subclass of
   * <code>ObjectOutputStream</code> that overrides this method, the
   * <code>resolveProxyClass</code> method in the corresponding subclass of
   * <code>ObjectInputStream</code> must read any data or objects written by
   * <code>annotateProxyClass</code>.
   *
   * @param cl the proxy class to annotate custom data for
   * @throws IOException any exception thrown by the underlying <code>OutputStream</code>
   * @see ObjectInputStream#resolveProxyClass(String[])
   * @since 1.3
   */
  protected void annotateProxyClass(Class<?> cl) throws IOException {
  }

  /**
   * This method will allow trusted subclasses of ObjectOutputStream to
   * substitute one object for another during serialization. Replacing
   * objects is disabled until enableReplaceObject is called. The
   * enableReplaceObject method checks that the stream requesting to do
   * replacement can be trusted.  The first occurrence of each object written
   * into the serialization stream is passed to replaceObject.  Subsequent
   * references to the object are replaced by the object returned by the
   * original call to replaceObject.  To ensure that the private state of
   * objects is not unintentionally exposed, only trusted streams may use
   * replaceObject.
   *
   * <p>The ObjectOutputStream.writeObject method takes a parameter of type
   * Object (as opposed to type Serializable) to allow for cases where
   * non-serializable objects are replaced by serializable ones.
   *
   * <p>When a subclass is replacing objects it must insure that either a
   * complementary substitution must be made during deserialization or that
   * the substituted object is compatible with every field where the
   * reference will be stored.  Objects whose type is not a subclass of the
   * type of the field or array element abort the serialization by raising an
   * exception and the object is not be stored.
   *
   * <p>This method is called only once when each object is first
   * encountered.  All subsequent references to the object will be redirected
   * to the new object. This method should return the object to be
   * substituted or the original object.
   *
   * <p>Null can be returned as the object to be substituted, but may cause
   * NullReferenceException in classes that contain references to the
   * original object since they may be expecting an object instead of
   * null.
   *
   * @param obj the object to be replaced
   * @return the alternate object that replaced the specified one
   * @throws IOException Any exception thrown by the underlying OutputStream.
   */
  protected Object replaceObject(Object obj) throws IOException {
    return obj;
  }

  /**
   * Enable the stream to do replacement of objects in the stream.  When
   * enabled, the replaceObject method is called for every object being
   * serialized.
   *
   * <p>If <code>enable</code> is true, and there is a security manager
   * installed, this method first calls the security manager's
   * <code>checkPermission</code> method with a
   * <code>SerializablePermission("enableSubstitution")</code> permission to
   * ensure it's ok to enable the stream to do replacement of objects in the
   * stream.
   *
   * @param enable boolean parameter to enable replacement of objects
   * @return the previous setting before this method was invoked
   * @throws SecurityException if a security manager exists and its <code>checkPermission</code>
   * method denies enabling the stream to do replacement of objects in the stream.
   * @see SecurityManager#checkPermission
   * @see java.io.SerializablePermission
   */
  protected boolean enableReplaceObject(boolean enable)
      throws SecurityException {
    if (enable == enableReplace) {
      return enable;
    }
    if (enable) {
      SecurityManager sm = System.getSecurityManager();
      if (sm != null) {
        sm.checkPermission(SUBSTITUTION_PERMISSION);
      }
    }
    enableReplace = enable;
    return !enableReplace;
  }

  /**
   * The writeStreamHeader method is provided so subclasses can append or
   * prepend their own header to the stream.  It writes the magic number and
   * version to the stream.
   *
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  protected void writeStreamHeader() throws IOException {
    bout.writeShort(STREAM_MAGIC);
    bout.writeShort(STREAM_VERSION);
  }

  /**
   * Write the specified class descriptor to the ObjectOutputStream.  Class
   * descriptors are used to identify the classes of objects written to the
   * stream.  Subclasses of ObjectOutputStream may override this method to
   * customize the way in which class descriptors are written to the
   * serialization stream.  The corresponding method in ObjectInputStream,
   * <code>readClassDescriptor</code>, should then be overridden to
   * reconstitute the class descriptor from its custom stream representation.
   * By default, this method writes class descriptors according to the format
   * defined in the Object Serialization specification.
   *
   * <p>Note that this method will only be called if the ObjectOutputStream
   * is not using the old serialization stream format (set by calling
   * ObjectOutputStream's <code>useProtocolVersion</code> method).  If this
   * serialization stream is using the old format
   * (<code>PROTOCOL_VERSION_1</code>), the class descriptor will be written
   * internally in a manner that cannot be overridden or customized.
   *
   * @param desc class descriptor to write to the stream
   * @throws IOException If an I/O error has occurred.
   * @see java.io.ObjectInputStream#readClassDescriptor()
   * @see #useProtocolVersion(int)
   * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
   * @since 1.3
   */
  protected void writeClassDescriptor(ObjectStreamClass desc)
      throws IOException {
    desc.writeNonProxy(this);
  }

  /**
   * Writes a byte. This method will block until the byte is actually
   * written.
   *
   * @param val the byte to be written to the stream
   * @throws IOException If an I/O error has occurred.
   */
  public void write(int val) throws IOException {
    bout.write(val);
  }

  /**
   * Writes an array of bytes. This method will block until the bytes are
   * actually written.
   *
   * @param buf the data to be written
   * @throws IOException If an I/O error has occurred.
   */
  public void write(byte[] buf) throws IOException {
    bout.write(buf, 0, buf.length, false);
  }

  /**
   * Writes a sub array of bytes.
   *
   * @param buf the data to be written
   * @param off the start offset in the data
   * @param len the number of bytes that are written
   * @throws IOException If an I/O error has occurred.
   */
  public void write(byte[] buf, int off, int len) throws IOException {
    if (buf == null) {
      throw new NullPointerException();
    }
    int endoff = off + len;
    if (off < 0 || len < 0 || endoff > buf.length || endoff < 0) {
      throw new IndexOutOfBoundsException();
    }
    bout.write(buf, off, len, false);
  }

  /**
   * Flushes the stream. This will write any buffered output bytes and flush
   * through to the underlying stream.
   *
   * @throws IOException If an I/O error has occurred.
   */
  public void flush() throws IOException {
    bout.flush();
  }

  /**
   * Drain any buffered data in ObjectOutputStream.  Similar to flush but
   * does not propagate the flush to the underlying stream.
   *
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  protected void drain() throws IOException {
    bout.drain();
  }

  /**
   * Closes the stream. This method must be called to release any resources
   * associated with the stream.
   *
   * @throws IOException If an I/O error has occurred.
   */
  public void close() throws IOException {
    flush();
    clear();
    bout.close();
  }

  /**
   * Writes a boolean.
   *
   * @param val the boolean to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeBoolean(boolean val) throws IOException {
    bout.writeBoolean(val);
  }

  /**
   * Writes an 8 bit byte.
   *
   * @param val the byte value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeByte(int val) throws IOException {
    bout.writeByte(val);
  }

  /**
   * Writes a 16 bit short.
   *
   * @param val the short value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeShort(int val) throws IOException {
    bout.writeShort(val);
  }

  /**
   * Writes a 16 bit char.
   *
   * @param val the char value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeChar(int val) throws IOException {
    bout.writeChar(val);
  }

  /**
   * Writes a 32 bit int.
   *
   * @param val the integer value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeInt(int val) throws IOException {
    bout.writeInt(val);
  }

  /**
   * Writes a 64 bit long.
   *
   * @param val the long value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeLong(long val) throws IOException {
    bout.writeLong(val);
  }

  /**
   * Writes a 32 bit float.
   *
   * @param val the float value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeFloat(float val) throws IOException {
    bout.writeFloat(val);
  }

  /**
   * Writes a 64 bit double.
   *
   * @param val the double value to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeDouble(double val) throws IOException {
    bout.writeDouble(val);
  }

  /**
   * Writes a String as a sequence of bytes.
   *
   * @param str the String of bytes to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeBytes(String str) throws IOException {
    bout.writeBytes(str);
  }

  /**
   * Writes a String as a sequence of chars.
   *
   * @param str the String of chars to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeChars(String str) throws IOException {
    bout.writeChars(str);
  }

  /**
   * Primitive data write of this String in
   * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
   * format.  Note that there is a
   * significant difference between writing a String into the stream as
   * primitive data or as an Object. A String instance written by writeObject
   * is written into the stream as a String initially. Future writeObject()
   * calls write references to the string into the stream.
   *
   * @param str the String to be written
   * @throws IOException if I/O errors occur while writing to the underlying stream
   */
  public void writeUTF(String str) throws IOException {
    bout.writeUTF(str);
  }

  /**
   * Provide programmatic access to the persistent fields to be written
   * to ObjectOutput.
   *
   * @since 1.2
   */
  public static abstract class PutField {

    /**
     * Put the value of the named boolean field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>boolean</code>
     */
    public abstract void put(String name, boolean val);

    /**
     * Put the value of the named byte field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>byte</code>
     */
    public abstract void put(String name, byte val);

    /**
     * Put the value of the named char field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>char</code>
     */
    public abstract void put(String name, char val);

    /**
     * Put the value of the named short field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>short</code>
     */
    public abstract void put(String name, short val);

    /**
     * Put the value of the named int field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>int</code>
     */
    public abstract void put(String name, int val);

    /**
     * Put the value of the named long field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>long</code>
     */
    public abstract void put(String name, long val);

    /**
     * Put the value of the named float field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>float</code>
     */
    public abstract void put(String name, float val);

    /**
     * Put the value of the named double field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not <code>double</code>
     */
    public abstract void put(String name, double val);

    /**
     * Put the value of the named Object field into the persistent field.
     *
     * @param name the name of the serializable field
     * @param val the value to assign to the field (which may be <code>null</code>)
     * @throws IllegalArgumentException if <code>name</code> does not match the name of a
     * serializable field for the class whose fields are being written, or if the type of the named
     * field is not a reference type
     */
    public abstract void put(String name, Object val);

    /**
     * Write the data and fields to the specified ObjectOutput stream,
     * which must be the same stream that produced this
     * <code>PutField</code> object.
     *
     * @param out the stream to write the data and fields to
     * @throws IOException if I/O errors occur while writing to the underlying stream
     * @throws IllegalArgumentException if the specified stream is not the same stream that produced
     * this <code>PutField</code> object
     * @deprecated This method does not write the values contained by this <code>PutField</code>
     * object in a proper format, and may result in corruption of the serialization stream.  The
     * correct way to write <code>PutField</code> data is by calling the {@link
     * java.io.ObjectOutputStream#writeFields()} method.
     */
    @Deprecated
    public abstract void write(ObjectOutput out) throws IOException;
  }


  /**
   * Returns protocol version in use.
   */
  int getProtocolVersion() {
    return protocol;
  }

  /**
   * Writes string without allowing it to be replaced in stream.  Used by
   * ObjectStreamClass to write class descriptor type strings.
   */
  void writeTypeString(String str) throws IOException {
    int handle;
    if (str == null) {
      writeNull();
    } else if ((handle = handles.lookup(str)) != -1) {
      writeHandle(handle);
    } else {
      writeString(str, false);
    }
  }

  /**
   * Verifies that this (possibly subclass) instance can be constructed
   * without violating security constraints: the subclass must not override
   * security-sensitive non-final methods, or else the
   * "enableSubclassImplementation" SerializablePermission is checked.
   */
  private void verifySubclass() {
    Class<?> cl = getClass();
    if (cl == ObjectOutputStream.class) {
      return;
    }
    SecurityManager sm = System.getSecurityManager();
    if (sm == null) {
      return;
    }
    processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
    WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
    Boolean result = Caches.subclassAudits.get(key);
    if (result == null) {
      result = Boolean.valueOf(auditSubclass(cl));
      Caches.subclassAudits.putIfAbsent(key, result);
    }
    if (result.booleanValue()) {
      return;
    }
    sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
  }

  /**
   * Performs reflective checks on given subclass to verify that it doesn't
   * override security-sensitive non-final methods.  Returns true if subclass
   * is "safe", false otherwise.
   */
  private static boolean auditSubclass(final Class<?> subcl) {
    Boolean result = AccessController.doPrivileged(
        new PrivilegedAction<Boolean>() {
          public Boolean run() {
            for (Class<?> cl = subcl;
                cl != ObjectOutputStream.class;
                cl = cl.getSuperclass()) {
              try {
                cl.getDeclaredMethod(
                    "writeUnshared", new Class<?>[]{Object.class});
                return Boolean.FALSE;
              } catch (NoSuchMethodException ex) {
              }
              try {
                cl.getDeclaredMethod("putFields", (Class<?>[]) null);
                return Boolean.FALSE;
              } catch (NoSuchMethodException ex) {
              }
            }
            return Boolean.TRUE;
          }
        }
    );
    return result.booleanValue();
  }

  /**
   * Clears internal data structures.
   */
  private void clear() {
    subs.clear();
    handles.clear();
  }

  /**
   * Underlying writeObject/writeUnshared implementation.
   */
  private void writeObject0(Object obj, boolean unshared)
      throws IOException {
    boolean oldMode = bout.setBlockDataMode(false);
    depth++;
    try {
      // handle previously written and non-replaceable objects
      int h;
      if ((obj = subs.lookup(obj)) == null) {
        writeNull();
        return;
      } else if (!unshared && (h = handles.lookup(obj)) != -1) {
        writeHandle(h);
        return;
      } else if (obj instanceof Class) {
        writeClass((Class) obj, unshared);
        return;
      } else if (obj instanceof ObjectStreamClass) {
        writeClassDesc((ObjectStreamClass) obj, unshared);
        return;
      }

      // check for replacement object
      Object orig = obj;
      Class<?> cl = obj.getClass();
      ObjectStreamClass desc;
      for (; ; ) {
        // REMIND: skip this check for strings/arrays?
        Class<?> repCl;
        desc = ObjectStreamClass.lookup(cl, true);
        if (!desc.hasWriteReplaceMethod() ||
            (obj = desc.invokeWriteReplace(obj)) == null ||
            (repCl = obj.getClass()) == cl) {
          break;
        }
        cl = repCl;
      }
      if (enableReplace) {
        Object rep = replaceObject(obj);
        if (rep != obj && rep != null) {
          cl = rep.getClass();
          desc = ObjectStreamClass.lookup(cl, true);
        }
        obj = rep;
      }

      // if object replaced, run through original checks a second time
      if (obj != orig) {
        subs.assign(orig, obj);
        if (obj == null) {
          writeNull();
          return;
        } else if (!unshared && (h = handles.lookup(obj)) != -1) {
          writeHandle(h);
          return;
        } else if (obj instanceof Class) {
          writeClass((Class) obj, unshared);
          return;
        } else if (obj instanceof ObjectStreamClass) {
          writeClassDesc((ObjectStreamClass) obj, unshared);
          return;
        }
      }

      // remaining cases
      if (obj instanceof String) {
        writeString((String) obj, unshared);
      } else if (cl.isArray()) {
        writeArray(obj, desc, unshared);
      } else if (obj instanceof Enum) {
        writeEnum((Enum<?>) obj, desc, unshared);
      } else if (obj instanceof Serializable) {
        writeOrdinaryObject(obj, desc, unshared);
      } else {
        if (extendedDebugInfo) {
          throw new NotSerializableException(
              cl.getName() + "\n" + debugInfoStack.toString());
        } else {
          throw new NotSerializableException(cl.getName());
        }
      }
    } finally {
      depth--;
      bout.setBlockDataMode(oldMode);
    }
  }

  /**
   * Writes null code to stream.
   */
  private void writeNull() throws IOException {
    bout.writeByte(TC_NULL);
  }

  /**
   * Writes given object handle to stream.
   */
  private void writeHandle(int handle) throws IOException {
    bout.writeByte(TC_REFERENCE);
    bout.writeInt(baseWireHandle + handle);
  }

  /**
   * Writes representation of given class to stream.
   */
  private void writeClass(Class<?> cl, boolean unshared) throws IOException {
    bout.writeByte(TC_CLASS);
    writeClassDesc(ObjectStreamClass.lookup(cl, true), false);
    handles.assign(unshared ? null : cl);
  }

  /**
   * Writes representation of given class descriptor to stream.
   */
  private void writeClassDesc(ObjectStreamClass desc, boolean unshared)
      throws IOException {
    int handle;
    if (desc == null) {
      writeNull();
    } else if (!unshared && (handle = handles.lookup(desc)) != -1) {
      writeHandle(handle);
    } else if (desc.isProxy()) {
      writeProxyDesc(desc, unshared);
    } else {
      writeNonProxyDesc(desc, unshared);
    }
  }

  private boolean isCustomSubclass() {
    // Return true if this class is a custom subclass of ObjectOutputStream
    return getClass().getClassLoader()
        != ObjectOutputStream.class.getClassLoader();
  }

  /**
   * Writes class descriptor representing a dynamic proxy class to stream.
   */
  private void writeProxyDesc(ObjectStreamClass desc, boolean unshared)
      throws IOException {
    bout.writeByte(TC_PROXYCLASSDESC);
    handles.assign(unshared ? null : desc);

    Class<?> cl = desc.forClass();
    Class<?>[] ifaces = cl.getInterfaces();
    bout.writeInt(ifaces.length);
    for (int i = 0; i < ifaces.length; i++) {
      bout.writeUTF(ifaces[i].getName());
    }

    bout.setBlockDataMode(true);
    if (cl != null && isCustomSubclass()) {
      ReflectUtil.checkPackageAccess(cl);
    }
    annotateProxyClass(cl);
    bout.setBlockDataMode(false);
    bout.writeByte(TC_ENDBLOCKDATA);

    writeClassDesc(desc.getSuperDesc(), false);
  }

  /**
   * Writes class descriptor representing a standard (i.e., not a dynamic
   * proxy) class to stream.
   */
  private void writeNonProxyDesc(ObjectStreamClass desc, boolean unshared)
      throws IOException {
    bout.writeByte(TC_CLASSDESC);
    handles.assign(unshared ? null : desc);

    if (protocol == PROTOCOL_VERSION_1) {
      // do not invoke class descriptor write hook with old protocol
      desc.writeNonProxy(this);
    } else {
      writeClassDescriptor(desc);
    }

    Class<?> cl = desc.forClass();
    bout.setBlockDataMode(true);
    if (cl != null && isCustomSubclass()) {
      ReflectUtil.checkPackageAccess(cl);
    }
    annotateClass(cl);
    bout.setBlockDataMode(false);
    bout.writeByte(TC_ENDBLOCKDATA);

    writeClassDesc(desc.getSuperDesc(), false);
  }

  /**
   * Writes given string to stream, using standard or long UTF format
   * depending on string length.
   */
  private void writeString(String str, boolean unshared) throws IOException {
    handles.assign(unshared ? null : str);
    long utflen = bout.getUTFLength(str);
    if (utflen <= 0xFFFF) {
      bout.writeByte(TC_STRING);
      bout.writeUTF(str, utflen);
    } else {
      bout.writeByte(TC_LONGSTRING);
      bout.writeLongUTF(str, utflen);
    }
  }

  /**
   * Writes given array object to stream.
   */
  private void writeArray(Object array,
      ObjectStreamClass desc,
      boolean unshared)
      throws IOException {
    bout.writeByte(TC_ARRAY);
    writeClassDesc(desc, false);
    handles.assign(unshared ? null : array);

    Class<?> ccl = desc.forClass().getComponentType();
    if (ccl.isPrimitive()) {
      if (ccl == Integer.TYPE) {
        int[] ia = (int[]) array;
        bout.writeInt(ia.length);
        bout.writeInts(ia, 0, ia.length);
      } else if (ccl == Byte.TYPE) {
        byte[] ba = (byte[]) array;
        bout.writeInt(ba.length);
        bout.write(ba, 0, ba.length, true);
      } else if (ccl == Long.TYPE) {
        long[] ja = (long[]) array;
        bout.writeInt(ja.length);
        bout.writeLongs(ja, 0, ja.length);
      } else if (ccl == Float.TYPE) {
        float[] fa = (float[]) array;
        bout.writeInt(fa.length);
        bout.writeFloats(fa, 0, fa.length);
      } else if (ccl == Double.TYPE) {
        double[] da = (double[]) array;
        bout.writeInt(da.length);
        bout.writeDoubles(da, 0, da.length);
      } else if (ccl == Short.TYPE) {
        short[] sa = (short[]) array;
        bout.writeInt(sa.length);
        bout.writeShorts(sa, 0, sa.length);
      } else if (ccl == Character.TYPE) {
        char[] ca = (char[]) array;
        bout.writeInt(ca.length);
        bout.writeChars(ca, 0, ca.length);
      } else if (ccl == Boolean.TYPE) {
        boolean[] za = (boolean[]) array;
        bout.writeInt(za.length);
        bout.writeBooleans(za, 0, za.length);
      } else {
        throw new InternalError();
      }
    } else {
      Object[] objs = (Object[]) array;
      int len = objs.length;
      bout.writeInt(len);
      if (extendedDebugInfo) {
        debugInfoStack.push(
            "array (class \"" + array.getClass().getName() +
                "\", size: " + len + ")");
      }
      try {
        for (int i = 0; i < len; i++) {
          if (extendedDebugInfo) {
            debugInfoStack.push(
                "element of array (index: " + i + ")");
          }
          try {
            writeObject0(objs[i], false);
          } finally {
            if (extendedDebugInfo) {
              debugInfoStack.pop();
            }
          }
        }
      } finally {
        if (extendedDebugInfo) {
          debugInfoStack.pop();
        }
      }
    }
  }

  /**
   * Writes given enum constant to stream.
   */
  private void writeEnum(Enum<?> en,
      ObjectStreamClass desc,
      boolean unshared)
      throws IOException {
    bout.writeByte(TC_ENUM);
    ObjectStreamClass sdesc = desc.getSuperDesc();
    writeClassDesc((sdesc.forClass() == Enum.class) ? desc : sdesc, false);
    handles.assign(unshared ? null : en);
    writeString(en.name(), false);
  }

  /**
   * Writes representation of a "ordinary" (i.e., not a String, Class,
   * ObjectStreamClass, array, or enum constant) serializable object to the
   * stream.
   */
  private void writeOrdinaryObject(Object obj,
      ObjectStreamClass desc,
      boolean unshared)
      throws IOException {
    if (extendedDebugInfo) {
      debugInfoStack.push(
          (depth == 1 ? "root " : "") + "object (class \"" +
              obj.getClass().getName() + "\", " + obj.toString() + ")");
    }
    try {
      desc.checkSerialize();

      bout.writeByte(TC_OBJECT);
      writeClassDesc(desc, false);
      handles.assign(unshared ? null : obj);
      if (desc.isExternalizable() && !desc.isProxy()) {
        writeExternalData((Externalizable) obj);
      } else {
        writeSerialData(obj, desc);
      }
    } finally {
      if (extendedDebugInfo) {
        debugInfoStack.pop();
      }
    }
  }

  /**
   * Writes externalizable data of given object by invoking its
   * writeExternal() method.
   */
  private void writeExternalData(Externalizable obj) throws IOException {
    PutFieldImpl oldPut = curPut;
    curPut = null;

    if (extendedDebugInfo) {
      debugInfoStack.push("writeExternal data");
    }
    SerialCallbackContext oldContext = curContext;
    try {
      curContext = null;
      if (protocol == PROTOCOL_VERSION_1) {
        obj.writeExternal(this);
      } else {
        bout.setBlockDataMode(true);
        obj.writeExternal(this);
        bout.setBlockDataMode(false);
        bout.writeByte(TC_ENDBLOCKDATA);
      }
    } finally {
      curContext = oldContext;
      if (extendedDebugInfo) {
        debugInfoStack.pop();
      }
    }

    curPut = oldPut;
  }

  /**
   * Writes instance data for each serializable class of given object, from
   * superclass to subclass.
   */
  private void writeSerialData(Object obj, ObjectStreamClass desc)
      throws IOException {
    ObjectStreamClass.ClassDataSlot[] slots = desc.getClassDataLayout();
    for (int i = 0; i < slots.length; i++) {
      ObjectStreamClass slotDesc = slots[i].desc;
      if (slotDesc.hasWriteObjectMethod()) {
        PutFieldImpl oldPut = curPut;
        curPut = null;
        SerialCallbackContext oldContext = curContext;

        if (extendedDebugInfo) {
          debugInfoStack.push(
              "custom writeObject data (class \"" +
                  slotDesc.getName() + "\")");
        }
        try {
          curContext = new SerialCallbackContext(obj, slotDesc);
          bout.setBlockDataMode(true);
          slotDesc.invokeWriteObject(obj, this);
          bout.setBlockDataMode(false);
          bout.writeByte(TC_ENDBLOCKDATA);
        } finally {
          curContext.setUsed();
          curContext = oldContext;
          if (extendedDebugInfo) {
            debugInfoStack.pop();
          }
        }

        curPut = oldPut;
      } else {
        defaultWriteFields(obj, slotDesc);
      }
    }
  }

  /**
   * Fetches and writes values of serializable fields of given object to
   * stream.  The given class descriptor specifies which field values to
   * write, and in which order they should be written.
   */
  private void defaultWriteFields(Object obj, ObjectStreamClass desc)
      throws IOException {
    Class<?> cl = desc.forClass();
    if (cl != null && obj != null && !cl.isInstance(obj)) {
      throw new ClassCastException();
    }

    desc.checkDefaultSerialize();

    int primDataSize = desc.getPrimDataSize();
    if (primVals == null || primVals.length < primDataSize) {
      primVals = new byte[primDataSize];
    }
    desc.getPrimFieldValues(obj, primVals);
    bout.write(primVals, 0, primDataSize, false);

    ObjectStreamField[] fields = desc.getFields(false);
    Object[] objVals = new Object[desc.getNumObjFields()];
    int numPrimFields = fields.length - objVals.length;
    desc.getObjFieldValues(obj, objVals);
    for (int i = 0; i < objVals.length; i++) {
      if (extendedDebugInfo) {
        debugInfoStack.push(
            "field (class \"" + desc.getName() + "\", name: \"" +
                fields[numPrimFields + i].getName() + "\", type: \"" +
                fields[numPrimFields + i].getType() + "\")");
      }
      try {
        writeObject0(objVals[i],
            fields[numPrimFields + i].isUnshared());
      } finally {
        if (extendedDebugInfo) {
          debugInfoStack.pop();
        }
      }
    }
  }

  /**
   * Attempts to write to stream fatal IOException that has caused
   * serialization to abort.
   */
  private void writeFatalException(IOException ex) throws IOException {
        /*
         * Note: the serialization specification states that if a second
         * IOException occurs while attempting to serialize the original fatal
         * exception to the stream, then a StreamCorruptedException should be
         * thrown (section 2.1).  However, due to a bug in previous
         * implementations of serialization, StreamCorruptedExceptions were
         * rarely (if ever) actually thrown--the "root" exceptions from
         * underlying streams were thrown instead.  This historical behavior is
         * followed here for consistency.
         */
    clear();
    boolean oldMode = bout.setBlockDataMode(false);
    try {
      bout.writeByte(TC_EXCEPTION);
      writeObject0(ex, false);
      clear();
    } finally {
      bout.setBlockDataMode(oldMode);
    }
  }

  /**
   * Converts specified span of float values into byte values.
   */
  // REMIND: remove once hotspot inlines Float.floatToIntBits
  private static native void floatsToBytes(float[] src, int srcpos,
      byte[] dst, int dstpos,
      int nfloats);

  /**
   * Converts specified span of double values into byte values.
   */
  // REMIND: remove once hotspot inlines Double.doubleToLongBits
  private static native void doublesToBytes(double[] src, int srcpos,
      byte[] dst, int dstpos,
      int ndoubles);

  /**
   * Default PutField implementation.
   */
  private class PutFieldImpl extends PutField {

    /**
     * class descriptor describing serializable fields
     */
    private final ObjectStreamClass desc;
    /**
     * primitive field values
     */
    private final byte[] primVals;
    /**
     * object field values
     */
    private final Object[] objVals;

    /**
     * Creates PutFieldImpl object for writing fields defined in given
     * class descriptor.
     */
    PutFieldImpl(ObjectStreamClass desc) {
      this.desc = desc;
      primVals = new byte[desc.getPrimDataSize()];
      objVals = new Object[desc.getNumObjFields()];
    }

    public void put(String name, boolean val) {
      Bits.putBoolean(primVals, getFieldOffset(name, Boolean.TYPE), val);
    }

    public void put(String name, byte val) {
      primVals[getFieldOffset(name, Byte.TYPE)] = val;
    }

    public void put(String name, char val) {
      Bits.putChar(primVals, getFieldOffset(name, Character.TYPE), val);
    }

    public void put(String name, short val) {
      Bits.putShort(primVals, getFieldOffset(name, Short.TYPE), val);
    }

    public void put(String name, int val) {
      Bits.putInt(primVals, getFieldOffset(name, Integer.TYPE), val);
    }

    public void put(String name, float val) {
      Bits.putFloat(primVals, getFieldOffset(name, Float.TYPE), val);
    }

    public void put(String name, long val) {
      Bits.putLong(primVals, getFieldOffset(name, Long.TYPE), val);
    }

    public void put(String name, double val) {
      Bits.putDouble(primVals, getFieldOffset(name, Double.TYPE), val);
    }

    public void put(String name, Object val) {
      objVals[getFieldOffset(name, Object.class)] = val;
    }

    // deprecated in ObjectOutputStream.PutField
    public void write(ObjectOutput out) throws IOException {
            /*
             * Applications should *not* use this method to write PutField
             * data, as it will lead to stream corruption if the PutField
             * object writes any primitive data (since block data mode is not
             * unset/set properly, as is done in OOS.writeFields()).  This
             * broken implementation is being retained solely for behavioral
             * compatibility, in order to support applications which use
             * OOS.PutField.write() for writing only non-primitive data.
             *
             * Serialization of unshared objects is not implemented here since
             * it is not necessary for backwards compatibility; also, unshared
             * semantics may not be supported by the given ObjectOutput
             * instance.  Applications which write unshared objects using the
             * PutField API must use OOS.writeFields().
             */
      if (ObjectOutputStream.this != out) {
        throw new IllegalArgumentException("wrong stream");
      }
      out.write(primVals, 0, primVals.length);

      ObjectStreamField[] fields = desc.getFields(false);
      int numPrimFields = fields.length - objVals.length;
      // REMIND: warn if numPrimFields > 0?
      for (int i = 0; i < objVals.length; i++) {
        if (fields[numPrimFields + i].isUnshared()) {
          throw new IOException("cannot write unshared object");
        }
        out.writeObject(objVals[i]);
      }
    }

    /**
     * Writes buffered primitive data and object fields to stream.
     */
    void writeFields() throws IOException {
      bout.write(primVals, 0, primVals.length, false);

      ObjectStreamField[] fields = desc.getFields(false);
      int numPrimFields = fields.length - objVals.length;
      for (int i = 0; i < objVals.length; i++) {
        if (extendedDebugInfo) {
          debugInfoStack.push(
              "field (class \"" + desc.getName() + "\", name: \"" +
                  fields[numPrimFields + i].getName() + "\", type: \"" +
                  fields[numPrimFields + i].getType() + "\")");
        }
        try {
          writeObject0(objVals[i],
              fields[numPrimFields + i].isUnshared());
        } finally {
          if (extendedDebugInfo) {
            debugInfoStack.pop();
          }
        }
      }
    }

    /**
     * Returns offset of field with given name and type.  A specified type
     * of null matches all types, Object.class matches all non-primitive
     * types, and any other non-null type matches assignable types only.
     * Throws IllegalArgumentException if no matching field found.
     */
    private int getFieldOffset(String name, Class<?> type) {
      ObjectStreamField field = desc.getField(name, type);
      if (field == null) {
        throw new IllegalArgumentException("no such field " + name +
            " with type " + type);
      }
      return field.getOffset();
    }
  }

  /**
   * Buffered output stream with two modes: in default mode, outputs data in
   * same format as DataOutputStream; in "block data" mode, outputs data
   * bracketed by block data markers (see object serialization specification
   * for details).
   */
  private static class BlockDataOutputStream
      extends OutputStream implements DataOutput {

    /**
     * maximum data block length
     */
    private static final int MAX_BLOCK_SIZE = 1024;
    /**
     * maximum data block header length
     */
    private static final int MAX_HEADER_SIZE = 5;
    /**
     * (tunable) length of char buffer (for writing strings)
     */
    private static final int CHAR_BUF_SIZE = 256;

    /**
     * buffer for writing general/block data
     */
    private final byte[] buf = new byte[MAX_BLOCK_SIZE];
    /**
     * buffer for writing block data headers
     */
    private final byte[] hbuf = new byte[MAX_HEADER_SIZE];
    /**
     * char buffer for fast string writes
     */
    private final char[] cbuf = new char[CHAR_BUF_SIZE];

    /**
     * block data mode
     */
    private boolean blkmode = false;
    /**
     * current offset into buf
     */
    private int pos = 0;

    /**
     * underlying output stream
     */
    private final OutputStream out;
    /**
     * loopback stream (for data writes that span data blocks)
     */
    private final DataOutputStream dout;

    /**
     * Creates new BlockDataOutputStream on top of given underlying stream.
     * Block data mode is turned off by default.
     */
    BlockDataOutputStream(OutputStream out) {
      this.out = out;
      dout = new DataOutputStream(this);
    }

    /**
     * Sets block data mode to the given mode (true == on, false == off)
     * and returns the previous mode value.  If the new mode is the same as
     * the old mode, no action is taken.  If the new mode differs from the
     * old mode, any buffered data is flushed before switching to the new
     * mode.
     */
    boolean setBlockDataMode(boolean mode) throws IOException {
      if (blkmode == mode) {
        return blkmode;
      }
      drain();
      blkmode = mode;
      return !blkmode;
    }

    /**
     * Returns true if the stream is currently in block data mode, false
     * otherwise.
     */
    boolean getBlockDataMode() {
      return blkmode;
    }

        /* ----------------- generic output stream methods ----------------- */
        /*
         * The following methods are equivalent to their counterparts in
         * OutputStream, except that they partition written data into data
         * blocks when in block data mode.
         */

    public void write(int b) throws IOException {
      if (pos >= MAX_BLOCK_SIZE) {
        drain();
      }
      buf[pos++] = (byte) b;
    }

    public void write(byte[] b) throws IOException {
      write(b, 0, b.length, false);
    }

    public void write(byte[] b, int off, int len) throws IOException {
      write(b, off, len, false);
    }

    public void flush() throws IOException {
      drain();
      out.flush();
    }

    public void close() throws IOException {
      flush();
      out.close();
    }

    /**
     * Writes specified span of byte values from given array.  If copy is
     * true, copies the values to an intermediate buffer before writing
     * them to underlying stream (to avoid exposing a reference to the
     * original byte array).
     */
    void write(byte[] b, int off, int len, boolean copy)
        throws IOException {
      if (!(copy || blkmode)) {           // write directly
        drain();
        out.write(b, off, len);
        return;
      }

      while (len > 0) {
        if (pos >= MAX_BLOCK_SIZE) {
          drain();
        }
        if (len >= MAX_BLOCK_SIZE && !copy && pos == 0) {
          // avoid unnecessary copy
          writeBlockHeader(MAX_BLOCK_SIZE);
          out.write(b, off, MAX_BLOCK_SIZE);
          off += MAX_BLOCK_SIZE;
          len -= MAX_BLOCK_SIZE;
        } else {
          int wlen = Math.min(len, MAX_BLOCK_SIZE - pos);
          System.arraycopy(b, off, buf, pos, wlen);
          pos += wlen;
          off += wlen;
          len -= wlen;
        }
      }
    }

    /**
     * Writes all buffered data from this stream to the underlying stream,
     * but does not flush underlying stream.
     */
    void drain() throws IOException {
      if (pos == 0) {
        return;
      }
      if (blkmode) {
        writeBlockHeader(pos);
      }
      out.write(buf, 0, pos);
      pos = 0;
    }

    /**
     * Writes block data header.  Data blocks shorter than 256 bytes are
     * prefixed with a 2-byte header; all others start with a 5-byte
     * header.
     */
    private void writeBlockHeader(int len) throws IOException {
      if (len <= 0xFF) {
        hbuf[0] = TC_BLOCKDATA;
        hbuf[1] = (byte) len;
        out.write(hbuf, 0, 2);
      } else {
        hbuf[0] = TC_BLOCKDATALONG;
        Bits.putInt(hbuf, 1, len);
        out.write(hbuf, 0, 5);
      }
    }


        /* ----------------- primitive data output methods ----------------- */
        /*
         * The following methods are equivalent to their counterparts in
         * DataOutputStream, except that they partition written data into data
         * blocks when in block data mode.
         */

    public void writeBoolean(boolean v) throws IOException {
      if (pos >= MAX_BLOCK_SIZE) {
        drain();
      }
      Bits.putBoolean(buf, pos++, v);
    }

    public void writeByte(int v) throws IOException {
      if (pos >= MAX_BLOCK_SIZE) {
        drain();
      }
      buf[pos++] = (byte) v;
    }

    public void writeChar(int v) throws IOException {
      if (pos + 2 <= MAX_BLOCK_SIZE) {
        Bits.putChar(buf, pos, (char) v);
        pos += 2;
      } else {
        dout.writeChar(v);
      }
    }

    public void writeShort(int v) throws IOException {
      if (pos + 2 <= MAX_BLOCK_SIZE) {
        Bits.putShort(buf, pos, (short) v);
        pos += 2;
      } else {
        dout.writeShort(v);
      }
    }

    public void writeInt(int v) throws IOException {
      if (pos + 4 <= MAX_BLOCK_SIZE) {
        Bits.putInt(buf, pos, v);
        pos += 4;
      } else {
        dout.writeInt(v);
      }
    }

    public void writeFloat(float v) throws IOException {
      if (pos + 4 <= MAX_BLOCK_SIZE) {
        Bits.putFloat(buf, pos, v);
        pos += 4;
      } else {
        dout.writeFloat(v);
      }
    }

    public void writeLong(long v) throws IOException {
      if (pos + 8 <= MAX_BLOCK_SIZE) {
        Bits.putLong(buf, pos, v);
        pos += 8;
      } else {
        dout.writeLong(v);
      }
    }

    public void writeDouble(double v) throws IOException {
      if (pos + 8 <= MAX_BLOCK_SIZE) {
        Bits.putDouble(buf, pos, v);
        pos += 8;
      } else {
        dout.writeDouble(v);
      }
    }

    public void writeBytes(String s) throws IOException {
      int endoff = s.length();
      int cpos = 0;
      int csize = 0;
      for (int off = 0; off < endoff; ) {
        if (cpos >= csize) {
          cpos = 0;
          csize = Math.min(endoff - off, CHAR_BUF_SIZE);
          s.getChars(off, off + csize, cbuf, 0);
        }
        if (pos >= MAX_BLOCK_SIZE) {
          drain();
        }
        int n = Math.min(csize - cpos, MAX_BLOCK_SIZE - pos);
        int stop = pos + n;
        while (pos < stop) {
          buf[pos++] = (byte) cbuf[cpos++];
        }
        off += n;
      }
    }

    public void writeChars(String s) throws IOException {
      int endoff = s.length();
      for (int off = 0; off < endoff; ) {
        int csize = Math.min(endoff - off, CHAR_BUF_SIZE);
        s.getChars(off, off + csize, cbuf, 0);
        writeChars(cbuf, 0, csize);
        off += csize;
      }
    }

    public void writeUTF(String s) throws IOException {
      writeUTF(s, getUTFLength(s));
    }


        /* -------------- primitive data array output methods -------------- */
        /*
         * The following methods write out spans of primitive data values.
         * Though equivalent to calling the corresponding primitive write
         * methods repeatedly, these methods are optimized for writing groups
         * of primitive data values more efficiently.
         */

    void writeBooleans(boolean[] v, int off, int len) throws IOException {
      int endoff = off + len;
      while (off < endoff) {
        if (pos >= MAX_BLOCK_SIZE) {
          drain();
        }
        int stop = Math.min(endoff, off + (MAX_BLOCK_SIZE - pos));
        while (off < stop) {
          Bits.putBoolean(buf, pos++, v[off++]);
        }
      }
    }

    void writeChars(char[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 2;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 1;
          int stop = Math.min(endoff, off + avail);
          while (off < stop) {
            Bits.putChar(buf, pos, v[off++]);
            pos += 2;
          }
        } else {
          dout.writeChar(v[off++]);
        }
      }
    }

    void writeShorts(short[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 2;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 1;
          int stop = Math.min(endoff, off + avail);
          while (off < stop) {
            Bits.putShort(buf, pos, v[off++]);
            pos += 2;
          }
        } else {
          dout.writeShort(v[off++]);
        }
      }
    }

    void writeInts(int[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 4;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 2;
          int stop = Math.min(endoff, off + avail);
          while (off < stop) {
            Bits.putInt(buf, pos, v[off++]);
            pos += 4;
          }
        } else {
          dout.writeInt(v[off++]);
        }
      }
    }

    void writeFloats(float[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 4;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 2;
          int chunklen = Math.min(endoff - off, avail);
          floatsToBytes(v, off, buf, pos, chunklen);
          off += chunklen;
          pos += chunklen << 2;
        } else {
          dout.writeFloat(v[off++]);
        }
      }
    }

    void writeLongs(long[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 8;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 3;
          int stop = Math.min(endoff, off + avail);
          while (off < stop) {
            Bits.putLong(buf, pos, v[off++]);
            pos += 8;
          }
        } else {
          dout.writeLong(v[off++]);
        }
      }
    }

    void writeDoubles(double[] v, int off, int len) throws IOException {
      int limit = MAX_BLOCK_SIZE - 8;
      int endoff = off + len;
      while (off < endoff) {
        if (pos <= limit) {
          int avail = (MAX_BLOCK_SIZE - pos) >> 3;
          int chunklen = Math.min(endoff - off, avail);
          doublesToBytes(v, off, buf, pos, chunklen);
          off += chunklen;
          pos += chunklen << 3;
        } else {
          dout.writeDouble(v[off++]);
        }
      }
    }

    /**
     * Returns the length in bytes of the UTF encoding of the given string.
     */
    long getUTFLength(String s) {
      int len = s.length();
      long utflen = 0;
      for (int off = 0; off < len; ) {
        int csize = Math.min(len - off, CHAR_BUF_SIZE);
        s.getChars(off, off + csize, cbuf, 0);
        for (int cpos = 0; cpos < csize; cpos++) {
          char c = cbuf[cpos];
          if (c >= 0x0001 && c <= 0x007F) {
            utflen++;
          } else if (c > 0x07FF) {
            utflen += 3;
          } else {
            utflen += 2;
          }
        }
        off += csize;
      }
      return utflen;
    }

    /**
     * Writes the given string in UTF format.  This method is used in
     * situations where the UTF encoding length of the string is already
     * known; specifying it explicitly avoids a prescan of the string to
     * determine its UTF length.
     */
    void writeUTF(String s, long utflen) throws IOException {
      if (utflen > 0xFFFFL) {
        throw new UTFDataFormatException();
      }
      writeShort((int) utflen);
      if (utflen == (long) s.length()) {
        writeBytes(s);
      } else {
        writeUTFBody(s);
      }
    }

    /**
     * Writes given string in "long" UTF format.  "Long" UTF format is
     * identical to standard UTF, except that it uses an 8 byte header
     * (instead of the standard 2 bytes) to convey the UTF encoding length.
     */
    void writeLongUTF(String s) throws IOException {
      writeLongUTF(s, getUTFLength(s));
    }

    /**
     * Writes given string in "long" UTF format, where the UTF encoding
     * length of the string is already known.
     */
    void writeLongUTF(String s, long utflen) throws IOException {
      writeLong(utflen);
      if (utflen == (long) s.length()) {
        writeBytes(s);
      } else {
        writeUTFBody(s);
      }
    }

    /**
     * Writes the "body" (i.e., the UTF representation minus the 2-byte or
     * 8-byte length header) of the UTF encoding for the given string.
     */
    private void writeUTFBody(String s) throws IOException {
      int limit = MAX_BLOCK_SIZE - 3;
      int len = s.length();
      for (int off = 0; off < len; ) {
        int csize = Math.min(len - off, CHAR_BUF_SIZE);
        s.getChars(off, off + csize, cbuf, 0);
        for (int cpos = 0; cpos < csize; cpos++) {
          char c = cbuf[cpos];
          if (pos <= limit) {
            if (c <= 0x007F && c != 0) {
              buf[pos++] = (byte) c;
            } else if (c > 0x07FF) {
              buf[pos + 2] = (byte) (0x80 | ((c >> 0) & 0x3F));
              buf[pos + 1] = (byte) (0x80 | ((c >> 6) & 0x3F));
              buf[pos + 0] = (byte) (0xE0 | ((c >> 12) & 0x0F));
              pos += 3;
            } else {
              buf[pos + 1] = (byte) (0x80 | ((c >> 0) & 0x3F));
              buf[pos + 0] = (byte) (0xC0 | ((c >> 6) & 0x1F));
              pos += 2;
            }
          } else {    // write one byte at a time to normalize block
            if (c <= 0x007F && c != 0) {
              write(c);
            } else if (c > 0x07FF) {
              write(0xE0 | ((c >> 12) & 0x0F));
              write(0x80 | ((c >> 6) & 0x3F));
              write(0x80 | ((c >> 0) & 0x3F));
            } else {
              write(0xC0 | ((c >> 6) & 0x1F));
              write(0x80 | ((c >> 0) & 0x3F));
            }
          }
        }
        off += csize;
      }
    }
  }

  /**
   * Lightweight identity hash table which maps objects to integer handles,
   * assigned in ascending order.
   */
  private static class HandleTable {

    /* number of mappings in table/next available handle */
    private int size;
    /* size threshold determining when to expand hash spine */
    private int threshold;
    /* factor for computing size threshold */
    private final float loadFactor;
    /* maps hash value -> candidate handle value */
    private int[] spine;
    /* maps handle value -> next candidate handle value */
    private int[] next;
    /* maps handle value -> associated object */
    private Object[] objs;

    /**
     * Creates new HandleTable with given capacity and load factor.
     */
    HandleTable(int initialCapacity, float loadFactor) {
      this.loadFactor = loadFactor;
      spine = new int[initialCapacity];
      next = new int[initialCapacity];
      objs = new Object[initialCapacity];
      threshold = (int) (initialCapacity * loadFactor);
      clear();
    }

    /**
     * Assigns next available handle to given object, and returns handle
     * value.  Handles are assigned in ascending order starting at 0.
     */
    int assign(Object obj) {
      if (size >= next.length) {
        growEntries();
      }
      if (size >= threshold) {
        growSpine();
      }
      insert(obj, size);
      return size++;
    }

    /**
     * Looks up and returns handle associated with given object, or -1 if
     * no mapping found.
     */
    int lookup(Object obj) {
      if (size == 0) {
        return -1;
      }
      int index = hash(obj) % spine.length;
      for (int i = spine[index]; i >= 0; i = next[i]) {
        if (objs[i] == obj) {
          return i;
        }
      }
      return -1;
    }

    /**
     * Resets table to its initial (empty) state.
     */
    void clear() {
      Arrays.fill(spine, -1);
      Arrays.fill(objs, 0, size, null);
      size = 0;
    }

    /**
     * Returns the number of mappings currently in table.
     */
    int size() {
      return size;
    }

    /**
     * Inserts mapping object -> handle mapping into table.  Assumes table
     * is large enough to accommodate new mapping.
     */
    private void insert(Object obj, int handle) {
      int index = hash(obj) % spine.length;
      objs[handle] = obj;
      next[handle] = spine[index];
      spine[index] = handle;
    }

    /**
     * Expands the hash "spine" -- equivalent to increasing the number of
     * buckets in a conventional hash table.
     */
    private void growSpine() {
      spine = new int[(spine.length << 1) + 1];
      threshold = (int) (spine.length * loadFactor);
      Arrays.fill(spine, -1);
      for (int i = 0; i < size; i++) {
        insert(objs[i], i);
      }
    }

    /**
     * Increases hash table capacity by lengthening entry arrays.
     */
    private void growEntries() {
      int newLength = (next.length << 1) + 1;
      int[] newNext = new int[newLength];
      System.arraycopy(next, 0, newNext, 0, size);
      next = newNext;

      Object[] newObjs = new Object[newLength];
      System.arraycopy(objs, 0, newObjs, 0, size);
      objs = newObjs;
    }

    /**
     * Returns hash value for given object.
     */
    private int hash(Object obj) {
      return System.identityHashCode(obj) & 0x7FFFFFFF;
    }
  }

  /**
   * Lightweight identity hash table which maps objects to replacement
   * objects.
   */
  private static class ReplaceTable {

    /* maps object -> index */
    private final HandleTable htab;
    /* maps index -> replacement object */
    private Object[] reps;

    /**
     * Creates new ReplaceTable with given capacity and load factor.
     */
    ReplaceTable(int initialCapacity, float loadFactor) {
      htab = new HandleTable(initialCapacity, loadFactor);
      reps = new Object[initialCapacity];
    }

    /**
     * Enters mapping from object to replacement object.
     */
    void assign(Object obj, Object rep) {
      int index = htab.assign(obj);
      while (index >= reps.length) {
        grow();
      }
      reps[index] = rep;
    }

    /**
     * Looks up and returns replacement for given object.  If no
     * replacement is found, returns the lookup object itself.
     */
    Object lookup(Object obj) {
      int index = htab.lookup(obj);
      return (index >= 0) ? reps[index] : obj;
    }

    /**
     * Resets table to its initial (empty) state.
     */
    void clear() {
      Arrays.fill(reps, 0, htab.size(), null);
      htab.clear();
    }

    /**
     * Returns the number of mappings currently in table.
     */
    int size() {
      return htab.size();
    }

    /**
     * Increases table capacity.
     */
    private void grow() {
      Object[] newReps = new Object[(reps.length << 1) + 1];
      System.arraycopy(reps, 0, newReps, 0, reps.length);
      reps = newReps;
    }
  }

  /**
   * Stack to keep debug information about the state of the
   * serialization process, for embedding in exception messages.
   */
  private static class DebugTraceInfoStack {

    private final List<String> stack;

    DebugTraceInfoStack() {
      stack = new ArrayList<>();
    }

    /**
     * Removes all of the elements from enclosed list.
     */
    void clear() {
      stack.clear();
    }

    /**
     * Removes the object at the top of enclosed list.
     */
    void pop() {
      stack.remove(stack.size() - 1);
    }

    /**
     * Pushes a String onto the top of enclosed list.
     */
    void push(String entry) {
      stack.add("\t- " + entry);
    }

    /**
     * Returns a string representation of this object
     */
    public String toString() {
      StringBuilder buffer = new StringBuilder();
      if (!stack.isEmpty()) {
        for (int i = stack.size(); i > 0; i--) {
          buffer.append(stack.get(i - 1) + ((i != 1) ? "\n" : ""));
        }
      }
      return buffer.toString();
    }
  }

}
